FIG. 3 shows a running portion of an ordinary crawler type vehicle. As shown, the running portion thereof is disposed with a driving wheel at one part of a truck frame 8 and with an idle wheel 10 at another part thereof, and is wrapped thereover with a crawler 11. For adjusting tension of the crawler 11, there is disposed an adjusting cylinder 1 via a buffer spring 12 within the truck frame 8 at the side of the idle wheel 10.
FIGS. 4 and 5 show exemplified structures having such an adjusting cylinder. The tension of the crawler is adjusted by adjusting the cylinder strokes by charing into or discharging a filling such as a grease out of the adjusting cylinder body 1. Therefore, a filling valve 4 for pouring the filling and a relief valve 5 for discharging it are disposed in the cylinder communicating with a grease passage 6, respectively (FIG. 4 shows an example where the valves 4,5 are placed in a piston portion 3, and FIG. 5 shows another example where the valves 4,5 are placed in a cylinder part 2).
Meantime, it has recently been found that the adjusting cylinder is effected with compressive load of pressure as high as from several ten to hundred tons, caused by getting foreign matters into the crawler while running (shown with (A) portions). When the cylinder receives the compressive load of such high pressure, the portion incorporated with the valves is compressively deformed, whereby a valve seat surface is deformed into an ellipse, the filling gets out of the cylinder and the adjustment about loosening of the crawler does not go ahead.
As a countermeasure thereagainst, it will be assumed that the tension adjusting cylinder is made large scaled so that the area of receiving the pressure due to the compressive load is increased, resulting in decreasing a compressive stress. However cost-up cannot be inevitably involved in company with making large scale, and the large scale is limited by sizes in running parts of the vehicle, and it is difficult to realize such a countermeasure.
Further, it may be also theoretically considered that the valves incorporated part is disposed outside of the adjusting cylinder body by such as a hose, however this is not an actual structure because an ultra high pressure is generated thereabout.
In view of the above mentioned circumstances of the prior art, the invention has been designed and is to provide an improved structure incorporated with the valves, in which the valves incorporated portion is prevented from the compressive deformation so as to avoid the leakage of the filling within the cylinder, so that the adjustment of the crawler may be well performed.